Fail-safe retardation sensing system



June 2, 1970 D. A. BRACKMAN i 3,515,071

FAIL-SAFE RETARDATION SENSING SYSTEM Filed April 8, 1968 2 Sheets-Sheet 1 w E5 g FORCE(Q) 4 INVENTOR.

2 DONALD A. BRACKMAN i BY MW 0 0.5 IO L5 2.0 M

TIME (Sec.)

ATTORNEY.

June 2, 1970 D. A. BRACKMAN 3,

FAIIrSAFE RETARDATION SENSING SYSTEM Filed April 8, 1968 Sheets-Sheet 2 SAFED POSITION INVENH )R. DONALD A. BRACK MAN BY 614 44, W

ATTORNEY.

United States Patent US. Cl. 10278 3 Claims ABSTRACT OF THE DISCLOSURE The invention is a safing and arming device designed for mounting in the nose well of high drag bombs. The device senses a failure of the drag system and thereupon initiates the operation of instrumentalities which prevent the fuze from arming, thus causing the bomb to fall as a dud. The device thus provides a fail-safe operation in the event of improper launch or in the event insufficient forces of deceleration are generated to cause the system to opcrate properly. The system mechanically senses an interruption of the desired forces of deceleration and blocks the eventual release of a preset mechanical timer so that the timer is prevented from performing its normally designed function of allowing the alignment of the explosive train by which the bomb is detonated.

The invention relates to military requirements for retarded bombs launched at low levels from high speed aircraft. Such bombs are fitted with high drag fins which, prior to launch, and when stored on board the aircraft, are folded against the bomb. Upon release the fins open up, thereby causing the bomb to decelerate at a greatly increased rate, so that they impact upon the target at a safe distance behind the launching aircraft.

Under these circumstances, the time between release and impact upon the target is very short. If in any case the proper retardation and resulting safe operation has not been achieved during this time, it is desirable that the bomb should disarm itself and fall as a dud, so that danger to the aircraft, which dropped the bomb, is avoided.

In such systems, the device is designed so that the forces of deceleration induced by the drag fins will cause the arming of the device. According to the invention, the failure of these forces to reach the required level is utilized to allow the bomb to become disarmed. In other words, the invention permits the bomb to be armed only after a minimum established rate of deceleration has been sensed for a minimum specified length of time. Failure to comply with this requirement should deactivate the fuze mechanism.

Accordingly, a principal object of the invention is to sense improper bomb drop environment and prevent the fuze from arming, thereby providing fail-safe operationtion.

Other objects and advantages of the invention will more clearly appear when reference is had to the accompanying drawings, in which:

FIG. 1 is a schematic view of a device embodying weights designed to be actuated by deceleration forces to arm a bomb or equivalent air delivered device to be actuated on delivery, in the condition the device is released by the aircraft;

FIG. 2 is a schematic view of the device of FIG. 1 after reaching the level at which it is committed to arm the device;

FIGS. 3, 3a and 3b are front, side and rear views of separate heavy and light gravity-actuated weights in assembly, designed according to the principles of the invention;

FIG. 4 is a graph showing deceleration plotted against 3,515,071 Patented June 2, 1970 time for a 750 pound bomb dropped at air speeds of 300, 400 and 500 knots;

FIG. 5 is a perspective view of an actual fuze constructed in accordance with the principles described in connection with FIGS. 3, 3a and 3b and showing the actuatng block separated from the carrier, with the fuze sa ed.

BACKGROUND The invention is embodied in a three mass sensing mechanism mounted in a suitable housing within the nose of the bomb which is released in the direction of the arrow A as illustrated in FIG. 1. These masses comprise a sensing weight 11, a gravity-actuated weight 12 hereinafter referred to as a G weight, and a timing block 13, which is actuated in conjunction with a run-away escapement delay as hereinafter described. A ball detent 15, carried in fixed cradle 15a holds the G weight in its initial position but releases it when permitted by the sensing weight 11.

The three masses are spring loaded as shown in FIG. 1 with sensing weight 11 held upwardly against the forces of gravity by compression spring 11a. This Weight, along with others hereinafter to be described will move in the direction of the motion of the arrow A when the specified deceleration is sensed. With the sensing weight 11 in its forward or advanced position with the spring 11a com pressed (see FIG. 2) the ball detent 15 holding the G weight 12 will effect its release so that it will be free to move forward to the bottom of the housing. The G weight 12 is controlled by two compression springs 16 and 17 and one extension spring 18, the combination spring load being adjusted to be of such a magnitude that the G weight can only move if the deceleration is above the threshold level at which the device is designed to operate. This action will occur very quickly after the fins have opened, normally within a fraction of a second.

It will be understood that the configuration of the bomb or similar air-delivered instrumentality, including the drag fins, and their operation upon release, and the mechanism through which the bomb is released, are well known in the art and since they form no part of the invention they will not be described herein.

Immediately after reaching the level at which the system commits itself to arm the fuze, the retardation sensing system will be aligned as shown in FIG. 2, with the extension spring 18 fully extended with the ball 15 locking sensing weight 11 down by moving into slot 19. Under these conditions, the G weight is bottomed against the end of the housing, with compression springs 16 and 17 depressed by the gravitational forces acting on the weight.

The relatively light timing block 13 is provided with a rack 20 which in turn engages a wheel 21 of the delay mechanism 14 of a run-away escapement type well known in the art. Due to its relatively low mass block 13 is affected relatively little by the forces of deceleration. It is, however, pulled by the extension spring 18 but its movement is resisted by the escape mechanism. Therefore, as long as the deceleration forces, as shown in the curves of FIG. 4, are larger than the spring forces acting on the G weight, the G weight will be held at the point of its farthest travel downwardly and the timing block 13 will continue its forward motion (downward in FIGS. 1 and 2) until the predetermined delay time, as controlled by the escapement mechanism, has expired. The system then releases the remaining fuze functions as the timing block locks down against the G weight and the fuze is armed in accordance with mechanical arrangements well known in the art.

The foregoing description covers the proper function of a retardation-actuated arming system. However, in the event of retarder failure as by the retarder accidentally breaking away from the bomb housing, retardation will not be continuous and effective under such circumstances, with the result that unstable conditions are created which makes it desirable to prevent the arming of the fuze in order to ensure that the bomb cannot be detonated if there is a possibility that proper aircraft to bomb separation has not been achieved.

When retarder failure occurs the following events take place. The deceleration will initially build up very quickly in a normal manner, as shown in FIG. 4, but when the retarders break away from the bomb or otherwise fail to become activated, the rate of retardation drops off radically. Moreover, the entire body of the bomb becomes unstable and may go into a spin or tumble as it falls. The centrifugal force resulting from the spin, particularly if the fuzing device is housed in the nose of the bomb, may replace the effect of deceleration and arm the bomb even though it was not decelerated properly. In such case it is desirable to disarm the bomb to avoid hazards to the launching aircraft and personnel, as previously noted.

As will be noted from the foregoing, the three mass system above described requires that the G weight be sufiiciently heavy to sense deceleration and stay forward (or down, as shown in the drawings) a sufficient time to pull the timing block for its full travel.

THE INVENTION I have devised an improved system which senses when a break away of the rearder occurs and uses this information to alter the fuze in such a manner that arming cannot occur. This is accomplished by providing a separable break away G weight which will separate the major heavy actuating mass from the spring system which is exerting force on the timing block when the failure of an adequate retarding force is sensed. With this arrangement, the sensitivity of the system to random forces is eliminated and the G level required to pull the timing block is increased far beyond that which occurs in any bomb flight. The precise construction of my separable weight system will now be described.

FIGS. 3, 3a and 3b show front, side and back views respectively, of a block similar in general configuration to the G weight 12 of FIGS. 1 and 2. This block is divided into a heavy, gravity-sensitive, actuating block 22 strapped to a much lighter carrier 23. The carrier 23 supports all the load of the compression springs 16 and 17, and extension spring 18, and the heavy portion 22 is strapped to the carrier by a latch-like finger 24 secured at the end of a spring arm 25 of the carrier 23. Cooperating with the latch 24 is a plate 26 which is cammed by a spring-pressed pin 27 (suitably mounted on the surrounding housing) when the pin is interposed against cam surface 28 of plate 26, in the event that deceleration forces fail to reach the preselected level.

With this construction, if the fins open properly and retardation is sensed, the system will function normally as previously described, and the carrier and heavy mass will act as a unit, since they are tied together, and will move downwardly as a unit by reason of the latch 24 holding the heavy mass integrally with the light weight carrier. As the assembly moves forward spring loaded pin 27 moves out behind the latch plate. In the event of loss of retarding force, the compression springs (16 and 17) will tend to return the combined weight and carrier to its original position but the spring loaded pin 27 will interpose itself in the path of cam surface 28 of plate 26,

moving latch 24 laterally and releasing the heavy mass 22 from the carrier.

The construction of FIGS. 3, 3a and 3b is more clearly shown in FIG. 5 which illustrates an actual fuze in its safed position, after spring loaded pin 27 has interposed itself in the path of cam surface 28 of cam 26 moving latch 24 laterally, as spring arm 25 is forced outwardly, with actuating mass 22 released from carrier 23.

It will thus be observed that if tumble develops and centrifugal or random forces act, the heavy mass can and does move forward independently without exerting any force on the spring system. This leaves only the light weight carrier 23 and timing block 13 to act against the heavy springs and since the springs are calibrated to work against the heavy mass the light weight carrier will be unable to generate sufiicient force to accomplish this function, and in consequence the fuze cannot arm itself and fails safe.

It will be appreciated that when the timing mechanism is properly triggered to begin the preset time delay takes place before the escapement reaches its terminal position, at which time well known mechanisms are actuated to detonate the bomb. Since these are not a part of the present invention they will not be described.

I claim:

1. In combination with an assembly comprising a triggerable device to be released and dropped from low flying aircraft, said device containing a weight-actuated delay mechanism for triggering it upon positive forward movement of said weight when the assembly is decelerated,

a carrier surrounding said weight,

a spring closed latch and cam means to spring said latch open for separating said weight from said carrier when the rate of deceleration is substantially decreased, whereby the delay mechanism is rendered inoperable.

2. The combination according to claim 1 in which said spring closed latch and cam means further comprises a spring arm securing said weight to said carrier, a cam on said arm, and a pin cooperating with said cam when said rate of deceleration is decreased to spring said arm away from said carrier.

3. The combination according to claim 1 in which said triggerable device is a high drag bomb and deceleration is caused by drag fins which open as the bomb is released, and the rendering inoperable of said delay mechanism causes the bomb to fail safe by falling as a dud under conditions where the desired environment of deceleration is not achieved.

References Cited UNITED STATES PATENTS 2,948,219 8/1960 Sapp 10278 3,316,841 5/1967 McFann et al. 10276 3,337,701 8/1967 Prebilic 102--4 XR 3,368,487 2/1968 OConnor et al. 10278 XR 3,415,191 12/1968 Meek et al. 10278 FOREIGN PATENTS 967,188 8/1964 Great Britain.

BENJAMIN A. BORCHELT, Primary Examiner T. H. WEBB, Assistant Examiner US. Cl. X.R. 

